Field of the Invention
The present invention generally relates to a printer and more particularly, to a printer apparatus of a page print type.
In recent years, a so-called page printer capable of printing at high quality and high speed as compared with the serial printer or the like, has come to be widely employed as a printing means for the information processing system.
The page printer as referred to above generally includes a data processing system which forms an output image data in a page unit based on a print data sent from an external host computer, and an image forming system which forms an image corresponding to the output image data on a paper sheet by a known electrophotographic process. The data processing system is constituted by a processor, a receiving buffer, and a bit map memory, etc., while the image forming system is constituted by an electrostatic latent image holder such as a photoreceptor drum, various chargers, a fixing device, and paper transport mechanisms, etc.
Upon turning on a power supply through operation of a power switch by an operator, the page printer is brought into a stand-by state waiting for input of print data (image data/control command) through initialization and warming up of various parts.
When the print data is inputted, the data processing system reads the print data in the order of reception, while storing said data in the receiving buffer, and draws the output image on a bit map memory through analysis of the control command, and after drawing of 1 page, reads out the output image data from the bit map memory for transfer thereof to the image forming system. In the case where the number of pages of the printing is in plurality, the data processing system immediately starts the drawing of the output image for the next page after transfer of the output image data for one page.
Meanwhile, along with the drawing of the output image, the image forming system takes out one sheet of copy paper from a paper cassette or the like for standing-by at a so-called register position in a transport passage, and thereafter, requests transfer of the output image data with respect to the date processing system. Upon receipt of the output image data, the image forming system starts formation of an electrostatic latent image, and successively transport copy paper sheets to a transfer position and a fixing position in timed relation to the progress of the image forming process thereafter for subsequent discharge of the copy paper sheet out of the printer.
In the data processing system of a conventional page printer, after completion of the drawing of the output image for one page (referred to as "bit map development" hereinafter), if the data transfer is not requested from the image forming system, the data processing system stands by, with substantial processing for the print data being suspended in a state where the output image on the bit map memory is maintained. In other words, even when the print data for the next page is present on the receiving buffer, the data processing system does not effect reading and bit map development thereof. However, storing of the print data into the receiving buffer is continued, and when the receiving buffer is filled up, notification of a busy state (i.e., state incapable of receiving) is given to the host unit.
Incidentally, in case where a state incapable of printing takes place due to "paper jamming" or "paper empty" in which the paper sheet accommodating cassette becomes empty, the image forming system of the page printer does not request data transfer to the data processing system until the trouble is removed.
More specifically, in the conventional arrangements, upon occurrence of the trouble in the image forming system, since reading of the receiving buffer is suspended at a time point when the bit map development for one page is completed, in the case where a large amount of print data exceeding the buffer capacity is inputted, the state of the page printer as observed from the host computer becomes busy, and when the working time for dealing with the trouble by the operator is included, such busy state is to continue for a comparatively long period of time.
Accordingly, in the conventional arrangements, there have been such problems that the completion of sending out the print data is undesirably delayed at the side of the host computer, thus resulting in lowering of the processing efficiency. Moreover, in the case where the host computer suspends sending out of the print data as a time out error processing at the time point when the busy allowable time has passed, even if the printing function is resumed through disappearance of the trouble in the image forming unit, no printing is effected with respect to the print data suspended to be sent out, and thus, the operator is required to give a printing instruction again to the host computer. Although an increase of the memory capacity for the receiving buffer may be considered for solving such a problem, there has been a limitation to the increase of capacity in the actual practice from the aspects of cost and space.